release-notes: drop references to kernel-fitimage

This commit drops references to the kernel-fitimage.bbclass to prevent
from build errors when the label is no longer available.

(From yocto-docs rev: 3610cfd76d1491d9ecff9816ab36df8d1b2a83c6)

Signed-off-by: Adrian Freihofer <adrian.freihofer@siemens.com>
Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/migration-guides/release-notes-5.1.rst

@@ -377,7 +377,7 @@ New Features / Enhancements in 5.1
       :term:`SIGGEN_EXCLUDERECIPES_ABISAFE` and does not trigger a rebuild on a
       change for dependent tasks.
 
-   -  In :ref:`ref-classes-kernel-fitimage`, the existence of
+   -  In ``kernel-fitimage``, the existence of
       :term:`EXTERNAL_KERNEL_DEVICETREE` is checked more thoroughly to avoid
       false positives.
 

documentation/migration-guides/release-notes-5.2.rst

@@ -29,7 +29,7 @@ New Features / Enhancements in |yocto-ver|
       ``RuntimeWatchdogSec`` option in ``/etc/systemd/system.conf``.
 
    -  :term:`FIT_UBOOT_ENV` to allow including a u-boot script as a text in a
-      fit image. See the :ref:`ref-classes-kernel-fitimage` for more information.
+      fit image. See the ``kernel-fitimage`` for more information.
 
    -  :ref:`ref-classes-meson`: :term:`MESON_INSTALL_TAGS` to allow passing
       install tags (``--tags``) to the ``meson install`` command during the
@@ -684,7 +684,7 @@ New Features / Enhancements in |yocto-ver|
       command-line tool was added to the different Yocto Project and OpenEmbedded
       repositories.
 
-   -  :ref:`ref-classes-kernel-fitimage`: handle :doc:`multiconfig
+   -  ``kernel-fitimage``: handle :doc:`multiconfig
       </dev-manual/multiconfig>` dependency when
       :term:`INITRAMFS_MULTICONFIG` is set.